The present invention relates to a bottom for fluidized beds, particularly for fluidized bed conveyors.
Fluidized bed conveyors are utilized for treating solid particulate materials, for example for the purposes of drying of wet refuse, regeneration of activated absorption media, or for performing chemical reaction such as gasification or burning of coal. The fluidized bed conveyors provide for intensive material exchange and heat exchange. A fluidizing gas flows in the fluidized bed conveyors advantageously in a vertical direction, whereas a material which is treated travels under the action of constant vertical whirling movement along the fluidized bed conveyor from its inlet to its outlet. In practice, it is desirable to attain particularly intensive mixing or particularly uniform whirling conditions in dependence upon each particular application of the fluidized bed conveyor.
Intensive whirling action is attained by essentially different speeds of a flow of the fluidizing gas at various locations of the fluidized bed. In contrast, especially uniform whirling conditions is attained when the speed of the fluidizing gas in each point of the fluidized bed conveyor is permanently maintained certain multiple times higher than the point whirling speed of a solid particulate material which is treated in the container. The required speed of fluidizing gas is generally equal to between 0.05 and 5.0 m/sec, and the temperature of fluidizing gas is generally equal to between 300.degree. K. and 1500.degree. K., in dependence upon grain size and density of material to be treated as well as upon temperature and characteristics of the fluidizing gas. It has been recognized that when the fluidizing gas has an especially high temperature, such as above 700.degree. K., fixedly set bottoms of the fluidized bed, particularly steel grates, are strongly warped. For this reason, they must be replaced, as a rule, when the fluidized bed is removed. The bottoms of metal alloys which have small thermal expansion reduce such warping; however, they are very expensive. On the other hand, in the case when solid particulate material is relatively heavy and thereby the fluidizing gas has a relatively high speed, it is recommended to provide for respectively heavier bottoms which excludes utilization of bottoms of solid layers. Finally, loosely placed bottoms have a further disadvantage that they are rarely correctly sealed at their edges, and thereby uncontrolled amounts of the fluidizing gas can enter the fluidized bed at these locations. Furthermore, the large bottoms such as massive grates are difficult to manipulate and cause difficulties during their replacement.